1. Field of the Invention
The present invention relates to a stacked inductor, more particularity, to a symmetrical stacked inductor made by a semiconductor process and applied to a radio frequency circuit.
2. Description of the Related Art
The rapid development of communication technology forced the communication market to expand and requires more channels. Presently, portable communication devices have developed into devices with high frequency, light, thin, short, small and multiple functions so that the requirement of high accuracy, exactitude, credibility and modularizing is needed. The effect of high frequency wireless communication focuses on the design of the radio frequency circuit, and the high frequency inductor of the radio frequency circuit requires a high quality factor(Q), high self-resonant frequency, low parasitic capacitance output and high stability, but it is hard to observe all factors during design.
Refer to FIG. 1, the conventional inductor 3, for example: a spiral inductor and a micro 3D inductor applied to a symmetrical circuit such as an LC voltage control oscillator (LC VCO) comprising two conventional inductors 3, two capacitors 5, a cross coupled circuit 7 and a tapped device 9. The design of the LC voltage control oscillator 1 must be symmetrical. If not, two conventional inductors have to be used for maintaining the symmetrical property of the oscillator circuit. The conventional design occupies a large area of the circuit layout, is expensive and is ineffective in decreasing phase noise.